Therapeutic reaction complex for muscle relaxation



June 13, 1963 J. F. GARDocKl ETAL 3,094,462

THERAPEUTIC REACTION COMPLEX FOR MUSCLE RELAXATION Filed sept. 1e, 1961 TIEN.. 4r

E. n.1 Tll 3,094,462 Patented June 18, 1963 ice 3,094,462 THERAPEUTIC REACTION COMPLEX FOR MUSCLE RELAXATION Joseph F. Gardocki, Doylestown, John W. Poole, Norristown, and George I. Poos, Ambler, Pa., assignors to McNeil Laboratories, Incorporated, a corporation of Pennsylvania Filed Sept. 18, 1961, Ser. No. 138,647 14 Claims. (Cl. 167-65) This invention relates to pharmaceutical compositions containing -chlorobenzoxazolinone, hereinafter referred to by its established and well-known generic name chlorzoxazone, and to methods for preparing and using such compositions.

Chlorzoxazone is a skeletal muscle relaxant whose principal site of action is on the reflex mechanisms involved in the production of skeletal muscle spasm. Chlorzoxazone acts on the spinal cord to inhibit transmission of nerve impulses through mfultisynaptic reilex arcs. This causes a reduction of muscle spasm with relief from pain and increased mobility of the involved muscles. The end result is more rapid recovery from painful muscle spasm with shorter periods of disability.

As in the case with most therapeutic agents of synthetic origin, the experimental pharmacologist and the clinician seek ways and means whereby dosage, no matter how low presently, can be reduced without interfering with the intended physiological effect. Studies are constantly being conducted on a wide variety of wellknown drugs with this object in mind. When successful, such studies obviously lead to considerable reduction in cost of medication to the patient as well as a substantial lessening or risks of drug reactionY with respect to 'those individuals who have peculiar idiosyncrasies toward synthetic substances. t

We have now discovered that a combination comprising chlorzoxazone and a 2-amino-SR,6R'chlorobenzox azole, or 5R,6R'-benzoxazolinone produces unexpected and surprising results following parenteral or oral administration. Not only is the per diem dose of chlorzoxazone required for producing muscle relaxation Vconsiderably reduced but, more importantly, the second component, i.e. the chlorobenzoxazole orthe benzoxazolinone, exerts a potentiating eiect upon the chlorzoxazone. Such potentiation of muscle relaxant activity is a completely unpredictable and surprising manifestando. The net effect of the novel combinationris that chlorzoxazone can be administered in substantially smaller doses, thus minimizing the possibility of sensitization 1Q reactionprone individuals and animals, while at lthe same time imparting the desired muscle relaxant effect.

The exact mechanism or cause of potentiating activity has not been established withY absolute certainty, but is believed to occur through one or more of several factors, including: True potentiation at the site of action; competition of the chlorzoxazone and benzoxazole (or 5R,6R, benzoxazolinone) componentsfor a hydroxylating enzyme system (the benzoxaaole-being the preferred substrate and chlorzoxazone-being spared); greater tissue uptake of chlorzoxazone, and complex formation of chlorzoxazone and the benzoxazole ingredient.

Intended to be included `among useful benzoxazole components Within the 2 amino 5R,6R' benzoxazole genus are those compounds wherein one of the R and R' substituents is halogen and the other is hydroxy, lower alkoxy or hydrogen. Halo substituents include chloro, bromo and iodo. Lower alkoxy groups include those containing from l to 6 carbon atoms, e.g. methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, pentoxy, isopentoxy, etc. By way of example, but not intended as a limitation, there may be cited the following: 2amino 5chlorobenzoxazo1e, Y2-amino-5-cl1loro-6-hydroxybenzoxazole,2-amino-S-chloro-G-methoxybenzoxazole. Similarly, the 5R,6R'benzoxazolinone component is one wherein the R substituent is halogen and the R' substituent is hydroxy or lower alkoxy, eg. such as one of those mentioned hereinabove. Y

The potentiating efect on chlorzoxazone and the resultant therapeutic activity may be accomplished either by means of physical admixture of the chlorzoxazone and 2amino5R,6R'-benzoxazole or SR,6R-benzoxazo linone or, alternatively, by means of a reaction prod-uct of chlorzoxazone and 2-amino-5R,6R'-benzoxazole. If it is elected to administer a physical admixt-ure, the ratio of the two essential components most suitable for obtaining the desired potentiating effect appears to be from .about 10:1 to about 1:1, the optimal limits being from about 8:1 to about 4:1, of chlorzoxazone:2amino- 5R,6R benzoxazole, or chlorzoxazone:5R,6R benzoxazolinone, as the case may be.

If it is desired xto administer a reaction product of chlorzoxazone and 2amino-5R,6R'benzoxazole, this may be readily accomplished by mixing equivalent quantities of the above ingredients in hot alkanol, eg, methyl alcohol or ethyl alcohol and crystallizing the product by cooling.

It will now be readily apparent to one skilled in the art that the drugs may be administered in combination, i.e. in physical combination in a single unitary dosage form; simultaneously, each in a separate dosage form; successively, i.e. a dosage of chlorzoxazone followed by a dose of 2-amino-5R,6Rbenzoxazole or 5R,6Rben zoxazolinone by the same or derent route of administration, or in the form of the above-described reaction product.

In preparing suitable physiologically acceptable dosageunit forms, any one of a wide variety of preparations may be formulated as, for example, tablets, capsules, pills, suspensions, emulsions, powders, etc. In addition to the therapeutically active components, there may be present additional substances commonly employed in the pharmaceutical art for preparing therapeutic compositions as, for example, excipients, binders, illers and other inert ingredients.

A convenient oral form for administration is the tablet, capsule or pill. A compressed tabletV containing 200 mgm. of chlorzoxazone and 50 mgm. of 2-amino5R,6R benzoxazole or 5R,6R'benzoxazolinone is an example of a suitable formulation. The fillers and binders which are commonly employed in the art of tablet compression may be used in formulating the tablets. As examples of these may be given corn starch, lactose, stearic acid, talc, magnesium stearate, etc. The quantities of these ingredients may vary widely in accordance with the dictates of those skilled in the a-rt and would depend largely upon the size and kind of tablet, i.e. soft or hard, which is required.

The method employed in assaying the muscle relaxant activity of the components, individually and in combination, was that of M. I. Orlofl, H. H. Williams and C. C.

Pfeiier [Proc Soc. Exp. Biol. and Med., 70:254 (1949)]. Briey, the method consisted of infusing a 0.5% metrazol solution at a rate of .05 cc./l sec. into the tail vein of male albino mice weighing 17 to 2l grams. This infusion results in a characteristic seizure pattern. The terminal portion of the pattern consists of a tonic convulsion. Standard muscle relaxants will convert the tonic convulsion to a clonic convulsion without altering the threshold volume and prolong the time of death after an infusion of a maximum volume of 1.0 cc. of a 0.5% `metrazol solution. The index of muscle relaxant activity employed was the percent conversion of the tonic to clonic convulsion in a group of ten mice which received the test preparation either orally or intraperitoneally.

Table I, below, shows the effect of chlorzoxazone and 2-amino5-chlorobenzoxazole singly and in various combinations and proportions on the metrazol seizure pattern (percent conversion, tonic to clonic convulsions) in male albino mice.

TABLE I Time in Minutes Post Drug, Percent Dose, Conversion Tonic-Clonle Drug Ine/ks.

Ghlorzoxazone- 400 0 90 100 20 0 0 0 200 0 40 60 20 0 0 0 100 0 20 0 (l 10 0 AzB A B Single Suspension 100 100 0 3l) 70 60 50 10 Reaction Product 100 100 0 50 100 l0 10 Separate Suspension 100 100 0 10D 50 100 50 10 0 Single Suspension D 50 t) B0 100 30 Separate Suspension 200 50 0 100 90 90 Q0 80 50 Single Suspension 100 25 D 20 60 3|) 50 0 10 Do 200 0 70 70 8l) 80 20 50 2-amino-5fchloro- {200 0 90 90 benzoxazole 100 0 10 40 10 0 0 l 10 mice/test period.

A chlorzoxazone. B =2-amtn0-Erchlorobenzoxazole.

From the above table it will be readily observed that combinations of chlorzoxazone and 2-amino-5-chloro benzoxazole, 100 mg. and 50 mg. per kg` and 100 mg. and 25 mg. per kg. are more potent than 100 mg. and 200 mg. per kg. of chlorzoxazone singly or 100 mg. per kg. of 2- amino-5chlorobenzoxazole singly. Too, it will be seen that combinations of chlorzoxazone and 2-amino-5 -chlorobenzoxazole in amounts, respectively, of 100 mg. and 100 mg. per kg., 200 mg. and 50 mg. per kg., and 200 and 25 mg. per kg. are more potent than 200 and 400 mg. per kg. of chlorzoxaaone singly, particularly to 180 minutes post drug. It will also be noted that a reaction product of chlorzoxazone and 2-amino-5-chlorobenzoxazole is more potent that 200 mg. and 400 mg. per kg. of chlorz/oxazone alone.

It can be concluded, on the basis of the data given in Table I, that the enhanced activity is due to true potentiation. For example, at 45 minutes post treatment, activity with 100 mg. per kg. of chlorzoxazone was 0 and with 100 rng. per kg. of 2-amino-5-chlorobenzoxazole it was l0. However, with a 100:100 mgJkg. ratio of chlorzoxazonezZ-amino 5 chlorobenzoxazole, activity was 50-60%, and with a 100:25 mg./kg. ratio, activity was 50%.

In order to demonstrate the potentiating effect on chlorzoxazone of a variety of substances within the framework of the genus 2-amino-5R,6Rbenzoxazole and the genus 5R,6Rbenzoxazolinone the following substances were combined with chlorzoxazone and the mixture tested for muscle relaxant activity: 2-amino-5-chloro 6 hydroxybenzoxazole; 5-chloro 6 hydroxybenzoxazolinone; 2- amino 5 chloro--methoxybenzoxazole. The procedure used was as described above, observations being made following intraperitoneal administration in male albino mice. The results are shown in Table II.

TABLE ll Percent Compound Dose, Time conversion mg./kg.,l.p. in Min. Tonic- Clonic and 25 15 8D It will be observed `from the data given above that chlorzoxazone and Z-amino-S-ohlorobenzoxazole in a combination of 100 mg. and 25 mg. per kg. respectively are equal in activity to 200 mg. per kg. of chlorzoxaz/one alone. Further, 2-amino-5-chloro--hydroxybenzoxazole, at a dose of 100 mg. per kg. is inactive at 15 minutes. In combination with 100 mg. per kg. of chlorzoxazone, 25 mg. per kg. of 2-amino-5-chloro6hydroxybenzoxazole is approximately equal to 200 mg. per kg. of chlorzoxazfone. It will also be noted that 200 mg. per kg. of 5ch1oro6 hydroxybenzoxazolinone is inactive whereas chlorzoxazone and 5-chloro--hydroxybenzoxazolinone, 100 mg. and 25 mg. per kg. respectively, at l5 minutes, is about equal to 200 mg. per kg. of 5chlorobenzoxa7lolnone. Finally, it will be obvious that 2-amino-5-chloro-6-methoxybenzoxazole is inactive singly at 15 minutes whereas chlorzoxazone and 2amino-5-chloro6methoxybenzox azole, 100 mg. and 25 mg. per kg. respectively, is approximately equal to 200 mg. per kg. of chlorzoxazone singly.

As noted above, election can be made between a physical admixture or a reaction product of the essential components, in order to obtain advantage of the potentiating etect on chlornoxazone. Turning now to the specie case of the reaction product of chlorzoxazone and 5- arnino-5R,6R'benzoxazole, substantial evidence has been obtained which leads to the conclusion that such reaction product is a complex moiety. Illustrative evidence of complex formation is `given in the following experiment:

Employing the technique ydescribed by John W. Poole and Takeru Higuchi [J.A.Ph.A. (Sc. Ed.) 48, No. 10, 592 (1959)), an excess amount of the drug being assayed was placed in a 60 ml. glass vial along with varying amounts of the second component, and the mixture shaken at 30 C. `for 16-20 hours in a constant temperature water bath. Distilled water was used as the solvent, the change in component content being `followed spectropho-tometrically. Phase diagram plots were constructed wherein (a) chlorzoxazone and (b) Z-amino-S-chlorobenzoxazole, respectively, were the drugs in excess.

In order that the nature of the invention with respect to complex formation may be more readily understood, reference is made to the accompanying illustrative drawings forming a part hereof in which:

FIG. I represents a phase diagram wherein chlorzoxazone is the drug in excess, 5.90 10'3 moles per liter, in the system. Plot was constructed from data in Table III.

FIG. II represents a phase diagram wherein Lamine-5- ohlorobenzoxazole is the drug in excess, 5.93 X10-a moles per liter. Plot was constructed from data Table IV.

TABLE III B Added to A in Solution System lil-3 l0-a rnoles per moles per liter liter TABLE IV A Added to B in Solution System 10-a 10-a moles per moles per liter liter From analyses of the phase diagrams, FIGS. I and II, and spectrophotometric assay of the solid complex (Poole et al., supra), the complex was determined to be composed of one molecule chlorzoxazone to one molecule of 2-amino-5-chlorobenzoxazole.

The following experiment shows further evidence of complexation when chlorzoxazone and 2amino5R,6R' benzoxazole are mixed in water: Equivalent quantities, 16.96 grams of chlorzoxazone and 16.86 grams of 2- amiuo5chlorobenzoxazole, were combined in a minimum amount of hot ethanol and the product crystallized rapidly by cooling. The product, obtained in 58% yield, melted at 189 C. to 189.5 C.; Nujol max. 2.93, 3.19, 3.40, 3.46, 5.47 (w.), 527 (w.), 5.66, 5.94, 6.14, 6.37, 6.72, 6.80, 724. Microanalysis supports a 1:1 complex: Caicd. for CH,C1,N,o,.c, 49.72; H, 2.68; N, 12.42; Cl, 20.97. Found.- C, 49.83; H, 2.79; N, 12.34; Cl, 29.74.

Next, mixtures of the two components were prepared and the following melting points were observed.

Percent B Percent A M.Pt., C.

6 t positioned to eil'ect two-point attachment with nucleophilic centers.

Example I A solution of cyanogen bromide in `200 parts by volume of methyl alcohol, prepared from 294.4 parts by weight of bromine and 90.2 parts by weight of sodium cyanide, is treated with a solution of 345 parts by weight of 2-amino 4-bron1ophenol in 12D() parts by volume of methyl alcohol. After stirring for one and one-half hours the reaction mixture is neutralized with ammonium hydroxide and poured into 5000 parts by volume of water. The crude product is filtered and air dried. After several recrystallizations from benzene-acetone using charcoal and nally benzene, there is obtained 2amino5bromo benzoxazole, melting point 180 C. to 1805* C. The calculated nitrogen content for CTHEBrNZO is N, 13.15% that found is N, 12.91%.

Example Il To la mixture of 16.8 parts by weight of Z-amino-S- chlorobenzoxazole and 7.9 parts by weight of pyridine in 500 parts by volume of dry benzene is added 7.8 parts by Weight of acetyl chloride. The reaction mixture is reuxed with stirring for four and one-half hours and allowed to stand overnight. Water is added and the solid material is collected by ltration. The solid is purified by crystallization from methanol to give white crystals of 2acetamido-5chlorobenzoxazole, melting point 220 C. to 220.5 C. The calculated nitrogen content of CgHqClNzOa is N, 13.30%; that found is N, 13.27%.

Example III A solution of 4-amino-6-ch1ororesorcinol is prepared by catalytically hydrogenating 17.3 parts by weight of 4-nitroso-6-chlororesorcinol in 100 parts by volume of methanol. To this solution is added a solution of 1.1.6 parts by weight of cyanogen bromide in 50 parts by volume of methanol. An oxygen-free nitrogen atmosphere is maintained throughout the reaction. After the addition is complete, the mixture is heated to boiling, cooled to room temperature and neutralized by the addition of an aqueous solution of sodium bicarbonate. Distillation under reduced pressure is carried out until approximately parts by volume of distillate is collected. The dark solid remaining in the ilask is collected by iiltration. Purification by rccrystallization from a mixture of acctonitrile and methanol gives white crystals of 2- amino-5chloroG-hydroxybenzoxazole, melting point 205 C. to 207 C. The calculated analysis for CqHEClNaO: is C, 45.54%; H, 2.73%; Cl, 19.21%; N, 19.21%. The values obtained are C, 45.71%; H, 2.64%; Cl, 19.23%; N, 410%.

Example IV A solution of 4-amino-6-chlororesorcinol in methanol is prepared as described in Example Ill and transferred under a nitrogen atmosphere yto a flask containing i8 parts by weight of sodium acetate and 100 parts by volume of ethyl acetate. A solution of 9.8 by weight of phosgene in 20 parts by volume of ethyl acetate is added with stirring while an atmosphere of oxygen-free nitrogen is maintained in the flask. Stirring is continued for one hour after the addition is complete and an equal volume of water is added. The non-aqueous layer is separated and Washed with aqueous sodium bicarbonate solution, dilute hydrochloric acid and finally with water. Evaporation of the organic layer leaves a red residue which is purified by crystallization from methanol with charcoal 'treatment to give White crystals of 5-chloro-6- hydroxy-Z-benzoxazolinone, melting point 245 C. to 247 C. 'I'he calculated nitrogen content for CqHrClNO, is N, 7.55%; that found is 7.34%.

Example V A 5 parts by weight sample of 2-amino-S-chloro-6- hydroxybenzoxazole is dissolved in a solution of 1.1 parts by weight of sodium hydroxide in 50 parts by volume of water. The resulting blue solution is treated with 0.4 part by weight of dimethylsulfate and the mixture is stirred at room temperature until it is neutral to litmus paper. The precipitated solid is collected by filtration and purified 'by crystallization from a mixture of acetone and benzene to give white crystals of 2-amino-5-chloro-6- methoxybenzoxazole. On heating, the product decomposes slowly from 195 C. to 215 C. The calculated nitrogen content of CBHqClNZOz is N, 14.15%; that found is N, 14.09%.

What is claimed is:

l. A reaction complex of chlorzoxazone land a member of the group consisting of 2amino5R,6R'-benzoxa zole wherein one of R and R' is halogen and the other is a member of the group consisting of hydrogen, hydroxy and lower alkoxy, and 5-halo-R-benzoxazolinone wherein R is a member of the group consisting of hydroxy and lower alkoxy.

2. A reaction complex of 5-chlorobenzoxazolinone and 2-amino-S-chlorobenzoxazole.

3. A reaction complex of 5-chlorobenzoxazolinone and 2-amino-5chloro-6-hydroxybenzoxazole.

4. A reaction complex of 5chlorobenzoxazolinone and 2-amino-5-chloro-6methoxybenzoxazole.

5. A reaction complex of 5-chlorobenzoxazolinone and 5-chloro6-hydroxybenzoxazolinone.

6. A new muscle relaxant composition containing 5- chlorobenzoxazolinone and a member of the group consisting of 2-amino-5R,6R'benzoxazole wherein one of R and R' is halogen and the other is a member of the group consisting of hydrogen, hydroxy and lower alkoxy, and 5-halo-6R-benzoxazolinone wherein R is a member of the group consisting of hydroxy and lower alkoxy.

7. The composition of claim 6 wherein the 5chloro benzoxazolinone:2 amino 5R,6R' benzoxazole is from about 10:1 to about 1:1.

8. 'I'he composition of claim 6 wherein the 5-chlorobenzoxazolinone:5halo6R-benzoxazolinone ratio is from about 10:1 to about 1:1.

9. A composition of matter comprising 5-chlorobenzoxazolinone in admixture with -amino5chlorobenzoxazole in ratio of from about 10:1 to about 1:1, respectively.

10. A composition of matter comprising S-chlorobenzoxazolinone in admixture with 2-amino-5-chloro-6-hydroxybenzoxazole in a ratio of from about 10:1 to about 1:1, respectively.

1l. A composition of matter comprising 5-ch1orobenzoxazolinone in admixture with 24amino-5-chloro-6- methoxybenzoxazole in a ratio of from about 10:1 to about 1:1, respectively.

12. A composition of matter comprising 5chloro benzoxazolinone in admixture with 5-chloro-6-hydroxybenzoxazolinone in a ratio of from about 10:1 to about 1:1, respectively.

13. A method for producing muscle relaxation which comprises administering to a living animal a reaction complex of 5-chlorobenzoxazolinone and 24amino-5R, 6Rbenzoxazole wherein one of R and R' is halogen and the other is a member of the group consisting of hydrogen, hydroxy and lower alkoxy, and 5halo6Rbenzox azolinone wherein R is a member of the group consisting of hydroxy and lower alkoxy.

14. A method for producing muscle relaxation which comprises administering to la living animal a physical mixture containing from about 1 part to about 10 parts of 5-cl1lorobenzoxazolinone and 1 part of 2-amino-5R, 6R'benzoxazole wherein one of R and R is halogen and the other is a member of the group consisting of hydrogen, hydroxy and lower alkoxy, and 5-ha1o-6Rbenzoxazolinone wherein R is a member of the group consisting of hydroxy and lower alkoxy.

References Cited in the file of this patent UNITED STATES PATENTS 2,890,985 Marsh June 16, 1959 2,895,877 Marsh June 21, 1959 FOREIGN PATENTS 599,362 Canada .lune 7, 1960 OTHER REFERENCES New and Nonotlcial Drugs, 1960, pp. 684-685. 

13. A METHOD FOR PRODUCING MUSCLE RELAXATION WHICH COMPRISES ADMINISTERING TO A LIVING ANIMAL A REACTION COMPLEX OF 5-CHLOROBENZOXAZOLINONE AND 2-AMINO-5R, 6R''-BENZOXAZOLE WHEREIN ONE OF R AND R'' IS HALOGEN AND THE OTHER IS A MEMBER OF THE GROUP CONSISTING OF HYDROGEN, HYDROXY AND LOWER ALKOXY, AND 5-HALO-6R-BENZOXAZOLINONE WHEREIN R IS A MEMBER OF THE GROUP CONSISTING OF HYDROXY AND LOWER ALKOXY. 